CN104362304A - A method for preparing Fe3O4/graphene lithium-ion battery composite negative electrode material in one step by high temperature solvothermal - Google Patents

Abstract

The invention discloses a method for preparing Fe ₃ O ₄ /graphene lithium-ion battery composite negative electrode material in one step by high-temperature solvent heat, which comprises the following steps: (1) selecting ferrous oxalate dihydrate, graphene and sodium acetate as reaction raw materials, and Add it into a high-temperature and high-pressure sealed stainless steel reaction kettle, then add an appropriate amount of ethylene glycol as a solvent to the stainless steel reaction kettle, and stir evenly; (2) After step (1) is completed, place the tightened stainless steel reaction kettle in the program Heating in an oven is controlled, the temperature is raised to 280-400° C., and the temperature is maintained at a constant temperature for 5-6 hours to prepare the Fe ₃ O ₄ /graphene lithium ion battery composite negative electrode material. The present invention is carried out in a high-temperature, high-pressure solvothermal environment, and the generated Fe ₃ O ₄ is directly compounded on the surface of graphene, and Fe ₃ O ₄ /graphene compound with complete crystal form and good electrochemical performance can be obtained without further calcination. Material.

Description

A method for preparing Fe3O4/graphene lithium-ion battery composite negative electrode material in one step by high temperature solvothermal

technical field

The invention relates to a preparation method of a novel lithium ion battery negative electrode material-Fe ₃ O ₄ /graphene composite material.

Background technique

Fe ₃ O ₄ , also known as magnetic iron oxide, is an inverse spinel crystal composed of Fe ²⁺ , Fe ³⁺ and O ^2- . Its theoretical capacity as a negative electrode material for lithium-ion batteries is 926mAh/g. The following electrode reactions can occur between Fe ₃ O ₄ and lithium ions: Li ₂ O can store and release ions reversibly, and has attracted extensive attention as a candidate to replace graphite anode materials due to its low cost and environmental friendliness.

The capacity of Fe ₃ O ₄ anode materials will decrease continuously due to the rapid volume change during charge and discharge, which hinders the practical application of Fe ₃ O ₄ .

Graphene is a flat film of hexagonal honeycomb lattice composed of carbon atoms with sp ² hybrid orbitals, and is a two-dimensional material with a thickness of only one carbon atom. Graphene has good electrical conductivity and its unique network sheet structure makes it an excellent carrier for electrode materials, and can alleviate the volume effect of Fe ₃ O ₄ .

The preparation method of Fe ₃ O ₄ /graphene composites mostly adopts the solvothermal method, but the existing solvothermal method generally reacts at a temperature lower than 200°C, and the reaction time is longer than 12 hours or even a few days, and the obtained product crystallizes. The density is low, and it is not tightly combined with the graphene substrate, and further high-temperature calcination and crystallization are often required, which not only prolongs the production cycle, but also wastes a lot of energy by high-temperature calcination.

Contents of the invention

Based on the above technical problems, the present invention provides a method for preparing Fe ₃ O ₄ /graphene lithium ion battery composite negative electrode material in one step by high temperature solvothermal.

The technical solution adopted in the present invention is:

A method for preparing Fe ₃ O ₄ /graphene lithium ion battery composite negative electrode material in one step by high temperature solvothermal, comprising the following steps:

(1) Select ferrous oxalate dihydrate, graphene and sodium acetate as reaction raw materials, add it in a high temperature resistant, high pressure airtight stainless steel reaction kettle, then add an appropriate amount of ethylene glycol as a solvent in the stainless steel reaction kettle, and stir evenly;

(2) After step (1) is completed, place the tightened stainless steel reaction kettle in a program-controlled oven for heating, raise the temperature to 280-400°C, and keep at this temperature for 5-6 hours to obtain Fe ₃ O ₄ /Graphene lithium ion battery composite anode material.

In step (1), the mass ratio of the ferrous oxalate dihydrate, graphene and sodium acetate is preferably 3:0.1:2.

In step (1), the stirring time is preferably 30-45 min.

In step (2), the heating rate is preferably 3-5°C/min.

In step (2), a post-processing step is preferably included, specifically as follows: centrifuge the black precipitate obtained from the reaction, wash with water and ethanol, and dry in vacuum to obtain the finished product.

Compared with other preparation techniques, the present invention has the following advantages:

(1) Due to the use of higher temperature and higher pressure than general solvothermal, there is no need for further calcination and crystallization steps, and a Fe ₃ O ₄ /graphene composite electrode with complete crystal form and good electrochemical performance can be obtained in one step reaction materials, effectively saving costs.

(2) Since the reaction is carried out at a higher temperature and higher pressure than the general solvent heat, the required reaction time is shorter than the general solvent heat, and the reaction can be as short as 6 hours at 280 ° C, and the crystal form can still be obtained Fe ₃ O ₄ /graphene composites with good and good electrochemical performance.

(3) Since the reaction is carried out under high temperature and high pressure conditions, the resulting Fe ₃ O ₄ particles attached to the surface of graphene have the advantages of uniform particle size and large specific surface area, and compared with the conventional solvothermal method, the obtained Fe _{3 O 4} O ₄ particle size is smaller, between 30-50nm.

(4) Ferrous oxalate dihydrate is selected as the iron source in the reaction raw materials. Compared with ferric chloride, etc., it has the advantages of low content of heteroatoms such as chloride ions and sulfate ions, non-melting at low temperatures, and carbonization and decomposition at high temperatures. It is beneficial to prepare Fe ₃ O ₄ /graphene composite material with good electrochemical performance.

(5) Since the reaction is carried out under conditions of higher temperature and higher pressure than general solvothermal, the obtained Fe ₃ O ₄ nanoparticles and graphene sheets are more tightly combined, and it is not easy to fall off or form agglomerates during charge and discharge. , thereby improving the specific capacity and cycle performance of the Fe ₃ O ₄ /graphene composite material as an electrode material for lithium-ion batteries. After testing, the Fe ₃ O ₄ /graphene composite material obtained by reacting at 280°C for 6 hours, under the current of 0.1C, the first discharge specific capacity is as high as 1270mAh g ^-1 , the charge specific capacity reaches 900mAh g ^-1 , and the discharge specific capacity after 65 cycles The capacity can still be maintained at 910mAh g ^-1 .

Description of drawings

The present invention will be further described below in conjunction with accompanying drawing and specific embodiment:

Fig. 1 is the X-ray diffraction (XRD) figure of embodiment 1 and embodiment 2 gained Fe ₃ O ₄ / graphene composite material;

Fig. 2 is the transmission electron microscope (TEM) figure of graphene sheet used;

Fig. 3 is the scanning electron micrograph (SEM) figure of the _Fe3O4 / _graphene composite material that embodiment 1 makes;

Fig. 4 is the scanning electron micrograph (SEM) figure of the _Fe3O4 /graphene composite material that _embodiment 2 makes;

Fig. 5 is the transmission electron microscope figure (TEM) figure of the _Fe3O4 /graphene composite material that embodiment 2 makes _;

Fig. 6 is the Raman spectrogram of the _Fe3O4 / _graphene composite material that embodiment 2 makes;

Fig. 7 is the thermogravimetric analysis figure (TGA) of the _Fe3O4 / _graphene composite material that embodiment 2 makes;

Fig. 8 is the infrared spectrum (IR) _figure of the _Fe3O4 /graphene composite material that embodiment 2 makes;

Fig. 9 is the first charge and discharge curve of the _Fe3O4 / _graphene composite material that embodiment 1 makes;

Fig. 10 is the first charge and discharge curve of the _Fe3O4 / _graphene composite material that embodiment 2 makes;

Fig. 11 is the first charge and discharge curve of the Fe ₃ O ₄ /graphene composite material prepared in Example 3.

Detailed ways

The present invention adopts high-temperature solvothermal method to prepare _Fe3O4 / _graphene lithium-ion battery composite negative electrode material in one step, specifically including the following steps:

(1) Select ferrous oxalate dihydrate, graphene and sodium acetate as reaction raw materials, the mass ratio of ferrous oxalate dihydrate, graphene and sodium acetate is 3:0.1:2, dissolve it in an appropriate amount of ethylene glycol solvent , and then transferred to a high-temperature, high-pressure sealed stainless steel reaction kettle, stirred for 30-45 minutes, so that the graphene, ferrous oxalate dihydrate and sodium acetate were evenly mixed.

(2) After step (1) is completed, place the tightened stainless steel reaction kettle in a program-controlled oven for heating, control the heating rate to 3-5°C/min, raise the temperature to 280-400°C, and keep at this temperature Constant temperature for 5-6 hours; after the reaction is completed, the black precipitate obtained from the reaction is separated by centrifugation, washed with water and ethanol, and dried in vacuum to obtain the finished Fe ₃ O ₄ /graphene lithium-ion battery composite negative electrode material.

The present invention heats the stainless steel reaction kettle to 280-400°C, and obtains greater pressure (the pressure in the kettle is generated by the vaporization of the solvent ethylene glycol at high temperature) to promote the reaction to proceed more vigorously, thus eliminating the need for additional calcination steps , a Fe ₃ O ₄ /graphene composite material with a good crystal form can be formed at a constant temperature for 6 hours, and the composite structure material has excellent electrochemical performance as an electrode material of a lithium ion battery.

The prepared Fe ₃ O ₄ /graphene composite material, acetylene black, and polyvinylidene fluoride (PVDF) were mixed in N-methylpyrrolidone at different mass ratios, and evenly coated on the copper foil. After vacuum drying at 120°C for 10 h, the positive electrode sheet was obtained by punching. The metal lithium sheet was used as the negative electrode, the Celgard 2300 microporous polypropylene membrane was used as the separator, and 1mol/L LiPF ₆ /EC:DEC:DMC (1:1:1) was The electrolyte was assembled into a battery in an argon atmosphere glove box. Wuhan Jinnuo LAND CT2001A battery charge and discharge tester was used to test its electrochemical performance at room temperature, and the charge and discharge voltage range was 0.01 to 3V.

The above-mentioned graphene is industrialized graphene oxide.

Example 1

(1) Weigh 0.3g of ferrous oxalate dihydrate, 0.01g of graphene and 0.2g of sodium acetate into 5ml of ethylene glycol, then transfer it to a high temperature and high pressure sealed stainless steel reaction kettle, and keep stirring For 30 minutes, the graphene was mixed evenly with ferrous oxalate dihydrate and sodium acetate.

(2) Heating the tightened stainless steel reaction kettle in a program-controlled heating box, the heating rate is controlled at 3-5°C/min, the solvent heat temperature is 230°C, and the constant temperature time is 12 hours to obtain Fe ₃ O with good crystal form ₄ /graphene composite material, wherein Fe ₃ O ₄ particles are rod-like structure. Using the Fe ₃ O ₄ /graphene composite material prepared under this condition as an active material, a button battery was assembled according to the method mentioned above, and its electrochemical performance was tested at room temperature to obtain specific capacity and cycle stability. Chemical performance indicators. The electrochemical performance of the composite material obtained under this condition is poor.

Example 2

(1) Weigh 0.3g of ferrous oxalate dihydrate, 0.01g of graphene and 0.2g of sodium acetate into 5ml of ethylene glycol, and then transfer it to a high-temperature, high-pressure airtight stainless steel reactor; mix the The final reaction raw materials were continuously stirred for 30 minutes, so that graphene was evenly mixed with ferrous oxalate dihydrate and sodium acetate.

(2) Heating the tightened stainless steel reaction kettle in a program-controlled heating box, the heating rate is controlled at 3-5°C/min, the solvent heat temperature is 280°C, and the constant temperature time is 6 hours to obtain Fe ₃ O with good crystal form ₄ /graphene composite material, wherein the Fe ₃ O ₄ particles are spherical. Using the Fe ₃ O ₄ /graphene composite material prepared under this condition as an active material, a button battery was assembled according to the method mentioned above, and its electrochemical performance was tested at room temperature to obtain specific capacity and cycle stability. Chemical performance indicators. The electrochemical performance of the composite material obtained under this condition is excellent.

Example 3

(1) Weigh 0.3g of ferrous oxalate dihydrate, 0.01g of graphene and 0.2g of sodium acetate into 5ml of ethylene glycol, and then transfer it to a high-temperature, high-pressure airtight stainless steel reactor; mix the The final reaction raw materials were continuously stirred for 30 minutes, so that graphene was evenly mixed with ferrous oxalate dihydrate and sodium acetate.

(2) Heating the tightened stainless steel reaction kettle in a program-controlled heating box, the heating rate is controlled at 3-5°C/min, the solvent heat treatment temperature is 310°C, and the constant temperature time is 6 hours to obtain Fe ₃ O with good crystal form ₄ /graphene composite material, wherein the Fe ₃ O ₄ particles are spherical. Using the Fe ₃ O ₄ /graphene composite material prepared under this condition as an active material, a button battery was assembled according to the method mentioned above, and its electrochemical performance was tested at room temperature to obtain specific capacity and cycle stability. Chemical performance indicators. The electrochemical performance of the composite material obtained under this condition is excellent.

Claims (5)

1. high-temperature solvent heat one step prepares Fe ₃o ₄the method of/graphene lithium ion battery composite negative pole material, is characterized in that comprising the following steps:

(1) choosing ferrous oxalate dihydrate, Graphene and sodium acetate is reaction raw materials, is added in the airtight stainless steel cauldron of high temperature resistant, high pressure, then in stainless steel cauldron, adds proper amount of glycol as solvent, stir;

(2) after step (1) completes, the stainless steel cauldron after tightening is placed in program control baking oven and heats, be warming up to 280 ~ 400 DEG C, and keep constant temperature 5 ~ 6h at this temperature, obtained Fe ₃o ₄/ graphene lithium ion battery composite negative pole material.

2. a kind of high-temperature solvent heat according to claim 1 one step prepares Fe ₃o ₄the method of/graphene lithium ion battery composite negative pole material, is characterized in that: in step (1), and the mass ratio of described ferrous oxalate dihydrate, Graphene and sodium acetate is 3:0.1:2.

3. a kind of high-temperature solvent heat according to claim 1 one step prepares Fe ₃o ₄the method of/graphene lithium ion battery composite negative pole material, is characterized in that: in step (1), and described mixing time is 30 ~ 45min.

4. a kind of high-temperature solvent heat according to claim 1 one step prepares Fe ₃o ₄the method of/graphene lithium ion battery composite negative pole material, is characterized in that: in step (2), and described heating rate is 3 ~ 5 DEG C/min.

5. a kind of high-temperature solvent heat according to claim 1 one step prepares Fe ₃o ₄the method of/graphene lithium ion battery composite negative pole material, it is characterized in that: step also comprises post-processing step in (2), specific as follows: gained black precipitate will be reacted by centrifugation, then through water and ethanol washing, and after vacuumize, get product.